7.2. How to deal with telecine and interlacing within NTSC DVDs

7.2.1. Introduction

What is telecine?
If you do not understand much of what is written in this document, read the
Wikipedia entry on telecine.
It is an understandable and reasonably comprehensive
description of what telecine is.

A note about the numbers.
Many documents, including the article linked above, refer to the fields
per second value of NTSC video as 59.94 and the corresponding frames
per second values as 29.97 (for telecined and interlaced) and 23.976
(for progressive). For simplicity, some documents even round these
numbers to 60, 30, and 24.

Strictly speaking, all those numbers are approximations. Black and
white NTSC video was exactly 60 fields per second, but 60000/1001
was later chosen to accommodate color data while remaining compatible
with contemporary black and white televisions. Digital NTSC video
(such as on a DVD) is also 60000/1001 fields per second. From this,
interlaced and telecined video are derived to be 30000/1001 frames
per second; progressive video is 24000/1001 frames per second.

Older versions of the MEncoder documentation
and many archived mailing list posts refer to 59.94, 29.97, and 23.976.
All MEncoder documentation has been updated
to use the fractional values, and you should use them too.

-ofps 23.976 is incorrect.
-ofps 24000/1001 should be used instead.

How telecine is used.
All video intended to be displayed on an NTSC
television set must be 60000/1001 fields per second. Made-for-TV movies
and shows are often filmed directly at 60000/1001 fields per second, but
the majority of cinema is filmed at 24 or 24000/1001 frames per
second. When cinematic movie DVDs are mastered, the video is then
converted for television using a process called telecine.

On a DVD, the video is never actually stored as 60000/1001 fields per
second. For video that was originally 60000/1001, each pair of fields is
combined to form a frame, resulting in 30000/1001 frames per
second. Hardware DVD players then read a flag embedded in the video
stream to determine whether the odd- or even-numbered lines should
form the first field.

Usually, 24000/1001 frames per second content stays as it is when
encoded for a DVD, and the DVD player must perform telecining
on-the-fly. Sometimes, however, the video is telecined
before being stored on the DVD; even though it
was originally 24000/1001 frames per second, it becomes 60000/1001 fields per
second. When it is stored on the DVD, pairs of fields are combined to form
30000/1001 frames per second.

When looking at individual frames formed from 60000/1001 fields per
second video, telecined or otherwise, interlacing is clearly visible
wherever there is any motion, because one field (say, the
even-numbered lines) represents a moment in time 1/(60000/1001)
seconds later than the other. Playing interlaced video on a computer
looks ugly both because the monitor is higher resolution and because
the video is shown frame-after-frame instead of field-after-field.

Notes:

This section only applies to NTSC DVDs, and not PAL.

The example MEncoder lines throughout the
document are not intended for
actual use. They are simply the bare minimum required to encode the
pertaining video category. How to make good DVD rips or fine-tune
libavcodec for maximal
quality is not within the scope of this section; refer to other
sections within the MEncoder encoding
guide.

There are a couple footnotes specific to this guide, linked like this:
[1]

7.2.2. How to tell what type of video you have

7.2.2.1. Progressive

Progressive video was originally filmed at 24000/1001 fps, and stored
on the DVD without alteration.

When you play a progressive DVD in MPlayer,
MPlayer will print the following line as
soon as the movie begins to play:

From this point forward, demux_mpg should never say it finds
"30000/1001 fps NTSC content."

When you watch progressive video, you should never see any
interlacing. Beware, however, because sometimes there is a tiny bit
of telecine mixed in where you would not expect. I have encountered TV
show DVDs that have one second of telecine at every scene change, or
at seemingly random places. I once watched a DVD that had a
progressive first half, and the second half was telecined. If you
want to be really thorough, you can scan the
entire movie:

mplayer dvd://1 -nosound -vo null -benchmark

Using -benchmark makes
MPlayer play the movie as quickly as it
possibly can; still, depending on your hardware, it can take a
while. Every time demux_mpg reports a framerate change, the line
immediately above will show you the time at which the change
occurred.

Sometimes progressive video on DVDs is referred to as
"soft-telecine" because it is intended to
be telecined by the DVD player.

7.2.2.2. Telecined

Telecined video was originally filmed at 24000/1001, but was telecined
before it was written to the DVD.

MPlayer does not (ever) report any
framerate changes when it plays telecined video.

Watching a telecined video, you will see interlacing artifacts that
seem to "blink": they repeatedly appear and disappear.
You can look closely at this by

mplayer dvd://1

Seek to a part with motion.

Use the . key to step forward one frame at a time.

Look at the pattern of interlaced-looking and progressive-looking
frames. If the pattern you see is PPPII,PPPII,PPPII,... then the
video is telecined. If you see some other pattern, then the video
may have been telecined using some non-standard method;
MEncoder cannot losslessly convert
non-standard telecine to progressive. If you do not see any
pattern at all, then it is most likely interlaced.

Sometimes telecined video on DVDs is referred to as
"hard-telecine". Since hard-telecine is already 60000/1001 fields
per second, the DVD player plays the video without any manipulation.

Another way to tell if your source is telecined or not is to play
the source with the -vf pullup and -v
command line options to see how pullup matches frames.
If the source is telecined, you should see on the console a 3:2 pattern
with 0+.1.+2 and 0++1
alternating.
This technique has the advantage that you do not need to watch the
source to identify it, which could be useful if you wish to automate
the encoding procedure, or to carry out said procedure remotely via
a slow connection.

7.2.2.3. Interlaced

Interlaced video was originally filmed at 60000/1001 fields per second,
and stored on the DVD as 30000/1001 frames per second. The interlacing effect
(often called "combing") is a result of combining pairs of
fields into frames. Each field is supposed to be 1/(60000/1001) seconds apart,
and when they are displayed simultaneously the difference is apparent.

As with telecined video, MPlayer should
not ever report any framerate changes when playing interlaced content.

When you view an interlaced video closely by frame-stepping with the
. key, you will see that every single frame is interlaced.

7.2.2.4. Mixed progressive and telecine

All of a "mixed progressive and telecine" video was originally
24000/1001 frames per second, but some parts of it ended up being telecined.

When MPlayer plays this category, it will
(often repeatedly) switch back and forth between "30000/1001 fps NTSC"
and "24000/1001 fps progressive NTSC". Watch the bottom of
MPlayer's output to see these messages.

You should check the "30000/1001 fps NTSC" sections to make sure
they are actually telecine, and not just interlaced.

7.2.2.5. Mixed progressive and interlaced

In "mixed progressive and interlaced" content, progressive
and interlaced video have been spliced together.

This category looks just like "mixed progressive and telecine",
until you examine the 30000/1001 fps sections and see that they do not have the
telecine pattern.

7.2.3. How to encode each category

As I mentioned in the beginning, example MEncoder
lines below are not meant to actually be used;
they only demonstrate the minimum parameters to properly encode each category.

7.2.3.1. Progressive

Progressive video requires no special filtering to encode. The only
parameter you need to be sure to use is -ofps 24000/1001.
Otherwise, MEncoder
will try to encode at 30000/1001 fps and will duplicate frames.

mencoder dvd://1 -oac copy -ovc lavc -ofps 24000/1001

It is often the case, however, that a video that looks progressive
actually has very short parts of telecine mixed in. Unless you are
sure, it is safest to treat the video as
mixed progressive and telecine.
The performance loss is small
[3].

7.2.3.2. Telecined

Telecine can be reversed to retrieve the original 24000/1001 content,
using a process called inverse-telecine.
MPlayer contains several filters to
accomplish this; the best filter, pullup, is described
in the mixed
progressive and telecine section.

7.2.3.3. Interlaced

For most practical cases it is not possible to retrieve a complete
progressive video from interlaced content. The only way to do so
without losing half of the vertical resolution is to double the
framerate and try to "guess" what ought to make up the
corresponding lines for each field (this has drawbacks - see method 3).

Encode the video in interlaced form. Normally, interlacing wreaks
havoc with the encoder's ability to compress well, but
libavcodec has two
parameters specifically for dealing with storing interlaced video a
bit better: ildct and ilme. Also,
using mbd=2 is strongly recommended
[2] because it
will encode macroblocks as non-interlaced in places where there is
no motion. Note that -ofps is NOT needed here.

mencoder dvd://1 -oac copy -ovc lavc -lavcopts ildct:ilme:mbd=2

Use a deinterlacing filter before encoding. There are several of
these filters available to choose from, each with its own advantages
and disadvantages. Consult mplayer -pphelp and
mplayer -vf help to see what is available
(grep for "deint"), read Michael Niedermayer's
Deinterlacing filters comparison,
and search the
MPlayer mailing lists to find many discussions about the
various filters.
Again, the framerate is not changing, so no
-ofps. Also, deinterlacing should be done after
cropping [1] and
before scaling.

mencoder dvd://1 -oac copy -vf yadif -ovc lavc

Unfortunately, this option is buggy with
MEncoder; it ought to work well with
MEncoder G2, but that is not here yet. You
might experience crashes. Anyway, the purpose of -vf
tfields is to create a full frame out of each field, which
makes the framerate 60000/1001. The advantage of this approach is that no
data is ever lost; however, since each frame comes from only one
field, the missing lines have to be interpolated somehow. There are
no very good methods of generating the missing data, and so the
result will look a bit similar to when using some deinterlacing
filters. Generating the missing lines creates other issues, as well,
simply because the amount of data doubles. So, higher encoding
bitrates are required to maintain quality, and more CPU power is
used for both encoding and decoding. tfields has several different
options for how to create the missing lines of each frame. If you
use this method, then Reference the manual, and chose whichever
option looks best for your material. Note that when using
tfields you
have to specify both
-fps and -ofps to be twice the
framerate of your original source.

If you plan on downscaling dramatically, you can extract and encode
only one of the two fields. Of course, you will lose half the vertical
resolution, but if you plan on downscaling to at most 1/2 of the
original, the loss will not matter much. The result will be a
progressive 30000/1001 frames per second file. The procedure is to use
-vf field, then crop
[1] and scale
appropriately. Remember that you will have to adjust the scale to
compensate for the vertical resolution being halved.

mencoder dvd://1 -oac copy -vf field=0 -ovc lavc

7.2.3.4. Mixed progressive and telecine

In order to turn mixed progressive and telecine video into entirely
progressive video, the telecined parts have to be
inverse-telecined. There are three ways to accomplish this,
described below. Note that you should
always inverse-telecine before any
rescaling; unless you really know what you are doing,
inverse-telecine before cropping, too
[1].
-ofps 24000/1001 is needed here because the output video
will be 24000/1001 frames per second.

-vf pullup is designed to inverse-telecine
telecined material while leaving progressive data alone. In order to
work properly, pullupmust
be followed by the softskip filter or
else MEncoder will crash.
pullup is, however, the cleanest and most
accurate method available for encoding both telecine and
"mixed progressive and telecine".

-vf filmdint is similar to
-vf pullup: both filters attempt to match a pair of
fields to form a complete frame. filmdint will
deinterlace individual fields that it cannot match, however, whereas
pullup will simply drop them. Also, the two filters
have separate detection code, and filmdint may tend to match fields a
bit less often. Which filter works better may depend on the input
video and personal taste; feel free to experiment with fine-tuning
the filters' options if you encounter problems with either one (see
the man page for details). For most well-mastered input video,
however, both filters work quite well, so either one is a safe choice
to start with.

mencoder dvd://1 -oac copy -vf filmdint -ovc lavc -ofps 24000/1001

An older method
is to, rather than inverse-telecine the telecined parts, telecine
the non-telecined parts and then inverse-telecine the whole
video. Sound confusing? softpulldown is a filter that goes through
a video and makes the entire file telecined. If we follow
softpulldown with either detc or
ivtc, the final result will be entirely
progressive. -ofps 24000/1001 is needed.

7.2.3.5. Mixed progressive and interlaced

There are two options for dealing with this category, each of
which is a compromise. You should decide based on the
duration/location of each type.

Treat it as progressive. The interlaced parts will look interlaced,
and some of the interlaced fields will have to be dropped, resulting
in a bit of uneven jumpiness. You can use a postprocessing filter if
you want to, but it may slightly degrade the progressive parts.

This option should definitely not be used if you want to eventually
display the video on an interlaced device (with a TV card, for
example). If you have interlaced frames in a 24000/1001 frames per
second video, they will be telecined along with the progressive
frames. Half of the interlaced "frames" will be displayed for three
fields' duration (3/(60000/1001) seconds), resulting in a flicking
"jump back in time" effect that looks quite bad. If you
even attempt this, you must use a
deinterlacing filter like lb or
l5.

It may also be a bad idea for progressive display, too. It will drop
pairs of consecutive interlaced fields, resulting in a discontinuity
that can be more visible than with the second method, which shows
some progressive frames twice. 30000/1001 frames per second interlaced
video is already a bit choppy because it really should be shown at
60000/1001 fields per second, so the duplicate frames do not stand out as
much.

Either way, it is best to consider your content and how you intend to
display it. If your video is 90% progressive and you never intend to
show it on a TV, you should favor a progressive approach. If it is
only half progressive, you probably want to encode it as if it is all
interlaced.

Treat it as interlaced. Some frames of the progressive parts will
need to be duplicated, resulting in uneven jumpiness. Again,
deinterlacing filters may slightly degrade the progressive parts.

7.2.4. Footnotes

About cropping:
Video data on DVDs are stored in a format called YUV 4:2:0. In YUV
video, luma ("brightness") and chroma ("color")
are stored separately. Because the human eye is somewhat less
sensitive to color than it is to brightness, in a YUV 4:2:0 picture
there is only one chroma pixel for every four luma pixels. In a
progressive picture, each square of four luma pixels (two on each
side) has one common chroma pixel. You must crop progressive YUV
4:2:0 to even resolutions, and use even offsets. For example,
crop=716:380:2:26 is OK but
crop=716:380:3:26 is not.

When you are dealing with interlaced YUV 4:2:0, the situation is a
bit more complicated. Instead of every four luma pixels in the
frame sharing a chroma pixel, every four luma
pixels in each field share a chroma
pixel. When fields are interlaced to form a frame, each scanline is
one pixel high. Now, instead of all four luma pixels being in a
square, there are two pixels side-by-side, and the other two pixels
are side-by-side two scanlines down. The two luma pixels in the
intermediate scanline are from the other field, and so share a
different chroma pixel with two luma pixels two scanlines away. All
this confusion makes it necessary to have vertical crop dimensions
and offsets be multiples of four. Horizontal can stay even.

For telecined video, I recommend that cropping take place after
inverse telecining. Once the video is progressive you only need to
crop by even numbers. If you really want to gain the slight speedup
that cropping first may offer, you must crop vertically by multiples
of four or else the inverse-telecine filter will not have proper data.

For interlaced (not telecined) video, you must always crop
vertically by multiples of four unless you use -vf
field before cropping.

About encoding parameters and quality:
Just because I recommend mbd=2 here does not mean it
should not be used elsewhere. Along with trell,
mbd=2 is one of the two
libavcodec options that
increases quality the most, and you should always use at least those
two unless the drop in encoding speed is prohibitive (e.g. realtime
encoding). There are many other options to
libavcodec that increase
encoding quality (and decrease encoding speed) but that is beyond
the scope of this document.

About the performance of pullup:
It is safe to use pullup (along with softskip
) on progressive video, and is usually a good idea unless
the source has been definitively verified to be entirely progressive.
The performance loss is small for most cases. On a bare-minimum encode,
pullup causes MEncoder to
be 50% slower. Adding sound processing and advanced lavcopts
overshadows that difference, bringing the performance
decrease of using pullup down to 2%.